Buried pipelines are commonly provided with systems to protect them from corrosion. Such protection systems generally include some form of cathodic protection. In such system, it is a general requirement to monitor the protection on a periodic basis to ensure sufficient protection is applied to prevent corrosion.
Generally there are two forms of cathodic protection in use today on pipelines. They include galvanic protection systems and impressed current systems. In galvanic systems, a sacrificial anode is used as the source of an electrical potential, which protects the pipeline. Galvanic protection systems are generally used primarily for short segments of pipe and in relatively conductive soils. In such systems, the segments of pipe are electrically isolated from each other and implementation of monitoring stations is relatively easy due to the low potential voltages, and small electrical currents. As the amount of pipeline increases and/or the conductivity of the soil decreases, a simple galvanic anode no longer suffices to provide protection.
As further understood by those of ordinary skill in the art, the sacrificial anodes (galvanic systems) are their own source, because as they dissolve they generate current. In other words, sacrificial anodes have very limited current capability but do not need a power source. Stated another way, sacrificial anodes are often used in short segments of pipe, while non-sacrificial anodes with ICCP (impressed current cathodic protection) are used to cover relatively longer segments of pipe which are too large to be covered by sacrificial anodes. In such instances, as understood by those of ordinary skill in the art, a DC supply is used between a pipe and a non-sacrificial anode since it cannot itself normally generate current.
Therefore, in instances where galvanic protection is inadequate, protections systems employing one or more transformer and rectifier systems are used to impress a protective electrical current on the pipeline. A number of transformers may be used and distributed along the pipeline to provide significant current to provide appropriate levels of protection. Because such systems are active, and protects significant amounts of pipe, a more rigorous monitoring system is required. At present, the industry standard practice for providing such monitoring frequently requires turning off the transformer for a short amount of time, typically for such as one second, to get an accurate measurement of the protection potential. This is due to the possible inaccuracies caused by interference between the monitoring system, and the current flow from the transformer injecting the protection current.
In addition, if there are numerous transformers, they need to be turned off synchronously to measure the protection. It would be advantageous, therefore, to provide a communications system to insure proper synchronization of the numerous transformers within a pipeline protection system during such measurement periods.
While various implementations of cathodic protection systems have been developed, and while various combinations of control systems have been developed, no design has emerged that generally encompasses all of the desired characteristics as hereafter presented in accordance with the subject technology.